Motion identification is useful in a very broad range of applications, including for example manufacturing production control, surveillance, and biomedical applications. Various methods have been developed by which motion can automatically be identified including mechanical, electronical, optical and acoustical motion detection.
For example, optical motion detection can be performed by a speckle-based technique, such as electronic speckle-pattern interferometry (ESPI). The ESPI has been used for displacement measurements and vibration analysis, aimed at amplitudes, slopes and modes of vibration. Speckle-based techniques have also been used for deformation measurement. The optical detection can be the only viable option if the environment of a moving object hinders sound propagation or unpredictably alters it.
The acoustical detection is especially useful in environments preventing light propagation from a moving object to an observer. For acoustical detection, the motion to be detected needs to be associated with a sound. However, the moving object's environment may not allow propagation of sound beyond a certain distance range. In particular, this occurs when sounds are produced behind a window (e.g. inside of a room). Likewise, motion of interest may be associated with sounds which may be remote or weak. If for any reason sounds decay before they reach a remote observer, sound detection should be indirect. This indirect detection may be based on optical means.
In particular, considering the example of sounds produced behind a window, they may be detected by detection of a laser beam reflection from the window. For generation of the reflection, the laser beam may be projected on the window. The reflection detection may be performed by an optical interferometer. The sounds then can be extracted (recognized) by processing the interferometer's output electronic signal. The interferometer's output is indicative of sounds produced behind the window because sounds vibrate the latter and phase-modulate the reflection of the laser beam. However, in this interference-based sound detection technique all sounds vibrating the window participate in the phase-modulation. Consequently, they are detected in sum (i.e. as superposition) and for their separation a blind source separation procedure needs to be performed. Also, in this technique, the projection laser and the detection interferometer module need to be placed in such a way that the specularly reflected beam is directed towards the detection module. This interference-based technique requires complicated calibration before the operation and error control during the operation.
Motion detection is useful in biomedical applications. For example, it can be used for detection and controlling Coronary Heart Disease (CHD). The CHD, along with Congestive Heart Failure, is connected with the regional and global motion of the left ventricle (LV) of the heart: CHD typically results in wall-motion abnormalities. For example, if local segments of the LV wall move weakly, this condition is known as hypokinesia; if they do not move at all, this condition is akinesia; and if they move out of sync with the rest of the heart, this condition is dyskinesia. Sometimes motion in multiple regions, or the entire heart, is compromised. The beats of LV can be imaged in a number of ways. The most common method of this is the echocardiogram—a test that uses sound waves to create a moving picture of the heart. In this test, high-frequency sound waves are emitted by a transducer placed on patient's ribs near the breast bone and directed toward the heart. The echoes of the sound waves are picked up and transformed as electrical impulses to an echocardiography machine. The machine converts these impulses into moving pictures of the heart.
Heart beats can be monitored by other methods, especially if less detailed picture is needed. For example, for the detection of heart rate and pulse there are three main techniques in use: (1) detecting blood flow in the capillaries of a finger or ear lobe with an infrared sensor; (2) detecting the heart ECG electrical signal in the hand area; and (3) detecting the heart ECG electrical signal with chest electrodes, commonly attached to an elastic strap going around the chest. A timing circuit measures the interval between each beat, averages the intervals for a short period of time and converts this into a heart rate reading expressed in beats per minute. Typically, a user of a heart rate monitor must stop exercising and hold his or her finger on the sensor and be very still, while measuring.